Heretofore, as one morphological image of an ultrasound image, a B-mode image (an image in which amplitude of an ultrasonic echo is represented by point luminance) representing a shape is used. In order to achieve high image quality of the B-mode image, a technique is suggested in which a sound speed value is corrected with focus data obtained by setting the sound speed of the subject, thereby improving the focus of the B-mode image. Furthermore, a measurement of a sound speed value in a portion of the subject (hereinafter, referred to as a local sound speed value) is tried.
For example, Patent Literature 1 discloses an ultrasound tomographic device in which focus calculation is performed using an input ultrasonic sound speed value as set sound speed of the whole device, and an ultrasound image is taken using the obtained focus data to correct the set ultrasonic sound speed value (that is, using an ambient sound speed value (hereinafter, sometimes referred to as an optimum sound speed value)), thereby improving the focus.
Patent Literature 2 discloses an ultrasound diagnostic device in which a lattice point set in a region shallower than a region of interest in a subject and an optimum sound speed value in the region of interest are determined using the Huygens principle, a reception wave received from the region of interest when an ultrasonic wave is transmitted toward the region of interest is calculated on the basis of the optimum sound speed value in the region of interest, an assumed sound speed in the region of interest is assumed, a reception wave from each lattice point obtained from the optimum sound speed value at each lattice point on the basis of the assumed sound speed is synthesized to obtain a synthesized reception wave, and a local sound speed value in the region of interest is decided on the basis of the reception wave and the synthesized reception wave.